An objective lens includes an aspherical lens facing a disk and having a predetermined first focal distance and a predetermined numerical aperture, and a holographic lens installed adjacent to the aspherical lens and having a second focal distance longer than that of the first focal distance and having a diffraction lattice to compensate for the chromatism due to a change in wavelength of laser light having a wavelength of 670 nm or less. Thus, during the shift between recoding and reproduction of a DVD or an HD-DVD, the change in wavelength due to the change in power of the laser light and chromatism according to the change can be effectively corrected. Also, since the objective lens is formed of one aspherical lens and one holographic lens, the material for each of the lenses can be easily selected and also the structure of the optical pickup using the objective lens according to the present invention can be simplified.
Legal claims defining the scope of protection, as filed with the USPTO.
1. An objective lens to focus light on a disk, comprising: an aspherical lens facing the disk, said aspherical lens having a predetermined first focal distance and a predetermined numerical aperture; and a holographic lens adjacent to said aspherical lens, said holographic lens having a second focal distance longer than the first focal distance and having a diffraction lattice that compensates for the chromatism due to a change in wavelength of laser light having a wavelength of 670 nm or less.
2. The objective lens as claimed in claim 1 , wherein the disk is either a DVD or an HD-DVD.
3. The objective lens as claimed in claim 1 , wherein said aspherical lens has a positive power, and said holographic lens has either a positive or a negative power.
4. The objective lens as claimed in claim 2 , wherein said aspherical lens has a positive power, and said holographic lens has either a positive or a negative power.
5. An optical pickup device for recording and/or reproducing to/from a disk, comprising: a light source to generate laser light which proceeds toward the disk; an objective lens including an aspherical lens facing the disk and having a predetermined first focal distance and a predetermined numerical aperture, and a holographic lens adjacent to the aspherical lens and having a second focal distance longer than the first focal distance and having a diffraction lattice to compensate for the chromatism due to a change in wavelength of a laser light having a wavelength of 670 nm or less; a beam splitter provided between said light source and said objective lens; and a photodetector that receives laser light reflected by the disk after passing through said beam splitter.
6. The device as claimed in claim 5 , wherein the disk is either a DVD or an HD-DVD.
7. The device as claimed in claim 4 , wherein said light source emits the laser light having a wavelength between and including 390 nm and 420 nm.
8. The device as claimed in claim 5 , wherein said light source emits the laser light having a wavelength between and including 390 nm and 420 nm.
9. The device as claimed in claim 4 , wherein the aspherical lens has a positive power and the holographic lens has either a positive or a negative power.
10. The device as claimed in claim 5 , wherein the aspherical lens has a positive power and the holographic lens has either a positive or a negative power.
11. The device as claimed in claim 6 , wherein the aspherical lens has a positive power and the holographic lens has either a positive or a negative power.
12. An optical pickup to record and/or reproduce to/from disks, comprising: first and second light sources to generate respective first and second laser lights having different wavelengths which proceed toward a respective one of two different kinds of disks; an objective lens including an aspherical lens facing the disk and having a predetermined first focal distance and a predetermined numerical aperture, and a holographic lens adjacent to the aspherical lens and having a second focal distance longer than that of the first focal distance and having a diffraction lattice to compensate for the chromatism due to a change in wavelength of laser light having a wavelength of 670 nm or less; a first beam splitter between said first light source and said objective lens to transmit the first and second laser lights emitted from said first and second light sources to the one of the disks; a second beam splitter between said first beam splitter and said first light source to reflect the second laser light emitted from said second light source to another of the disks; and a photodetector to receive the first and second laser lights reflected by either of the disks and said first beam splitter.
13. The optical pickup as claimed in claim 12 , wherein the different kinds of disks are a DVD and an HD-DVD.
14. The optical pickup as claimed in claim 12 , wherein said first light source emits a first laser light having a wavelength between and including 390 nm and 420 nm, and said second light source emits a second laser light having a wavelength between and including 630 nm and 670 nm.
15. The optical pickup as claimed in claim 13 , wherein said first light source emits a first laser light having a wavelength between and including 390 nm and 420 nm, and said second light source emits a second laser light having a wavelength between and including 630 nm and 670 nm.
16. The optical pickup as claimed in claim 14 , wherein said first light source emits a first laser light having a wavelength of 405 nm and said second light source emits a second laser light having a wavelength of 650 nm.
17. The optical pickup as claimed in claim 12 , wherein the aspherical lens has positive power and the holographic lens has either a positive or a negative power.
18. The optical pickup as claimed in claim 13 , wherein the aspherical lens has positive power and the holographic lens has either a positive or a negative power.
19. The optical pickup as claimed in claim 16 , wherein the aspherical lens has positive power and the holographic lens has either a positive or a negative power.
20. The optical pickup as claimed in claim 14 , wherein the aspherical lens has positive power and the holographic lens has either a positive or a negative power.
21. An objective lens to focus light on a disk, comprising: a holographic lens; and an aspherical lens between said holographic lens and the disk, said aspherical lens being at a fixed position relative to the disk so as to compensate for the chromatism due to a change in wavelength of the laser light having a wavelength of 670 nm or less.
22. The objective lens as claimed in claim 21 , wherein said holographic lens and said aspherical lens compensates for the chromatism so as to produce a wave surface chromatism of less than 0.1 .
23. The objective lens as claimed in claim 21 , wherein said aspherical lens comprises a predetermined first focal distance, and said holographic lens comprises a second focal distance longer than the first focal distance.
24. The objective lens as claimed in claim 21 , wherein said aspherical lens has a positive power, and said holographic lens has a positive power.
25. The objective lens as claimed in claim 21 , wherein said aspherical lens has a positive power, and said holographic lens has a negative power.
26. The objective lens as claimed in claim 21 , wherein the change in wavelength is 2 nm.
27. An optical pickup to record and/or reproduce to/from a disk, comprising: a light source to generate laser light which proceeds toward the disk; an objective lens comprising a holographic lens, and an aspherical lens between the holographic lens and the disk, the aspherical lens being at a fixed position relative to the disk so as to compensate for the chromatism due to a change in wavelength of the laser light having a wavelength of 670 nm or less; and a photodetector that receives laser light reflected by the disk.
28. The optical pickup as claimed in claim 27 , wherein said objective lens compensates for the chromatism so as to produce a wave surface chromatism of less than 0.1 .
29. The optical pickup as claimed in claim 27 , wherein the aspherical lens comprises a predetermined first focal distance, and the holographic lens comprises a second focal distance longer than the first focal distance.
30. The optical pickup as claimed in claim 27 , wherein the aspherical lens has a positive power, and the holographic lens has a positive power.
31. The optical pickup as claimed in claim 27 , wherein the aspherical lens has a positive power, and the holographic lens has a negative power.
32. The optical pickup as claimed in claim 27 , wherein the change in wavelength is 2 nm.
33. An optical pickup to record and/or reproduce to/from disks, comprising: light sources to generate laser lights having different wavelengths which proceed toward respective ones of the disks, depending upon which one of the disks is to be accessed; an objective lens comprising a holographic lens, and an aspherical lens between the holographic lens and the disk to be accessed, the aspherical lens being at fixed positions relative to the disk to be accessed so as to compensate for the chromatism due to a change in wavelength of the laser lights having a wavelength of 670 nm or less; and a photodetector to receive the laser light reflected by the disk to be accessed.
34. The optical pickup as claimed in claim 33 , further comprising an optical adjusting unit to move the aspherical lens between the fixed positions based upon the wavelength of the generated laser light.
35. The optical pickup as claimed in claim 33 , wherein said objective lens compensates for the chromatism so as to produce a wave surface chromatism of less than 0.1 .
36. The optical pickup as claimed in claim 33 , wherein the aspherical lens comprises a predetermined first focal distance, and the holographic lens comprises a second focal distance longer than the first focal distance.
37. The optical pickup as claimed in claim 33 , wherein the aspherical lens has a positive power, and the holographic lens has a positive power.
38. The optical pickup as claimed in claim 33 , wherein the aspherical lens has a positive power, and the holographic lens has a negative power.
39. The optical pickup as claimed in claim 33 , wherein the change in wavelength is 2 nm.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
February 28, 2001
January 13, 2004
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